io\_uring\_prep\_readv\_fixed(3) liburing Manual io\_uring\_prep\_readv\_fixed(3)

# [NAME](#NAME)

io\_uring\_prep\_readv\_fixed - prepare a vectored read using fixed buffers

# [SYNOPSIS](#SYNOPSIS)

```
#include <liburing.h>
```

```
void io_uring_prep_readv_fixed(struct io_uring_sqe *sqe,
                               int fd,
                               const struct iovec *iovecs,
                               unsigned nr_vecs,
                               __u64 offset,
                               int flags,
                               int buf_index);
```

# [DESCRIPTION](#DESCRIPTION)

The [**io\_uring\_prep\_readv\_fixed**(3)](/man/os/liburing/io_uring_prep_readv_fixed.3) function prepares a vectored read request using fixed (registered) buffers. The submission queue entry *sqe* is setup to use the file descriptor *fd* to start reading *nr\_vecs* iovecs from the file position *offset*.

The *iovecs* argument points to an array of iovec structures describing the read buffers. All buffers must be part of the registered buffer set at index *buf\_index*, previously registered with [**io\_uring\_register\_buffers**(3)](/man/os/liburing/io_uring_register_buffers.3).

The *flags* argument can contain any per-request flags, such as **RWF\_NOWAIT** or other flags supported by [**preadv2**(2)](/man/os/liburing/preadv2.2).

Using fixed buffers avoids the overhead of mapping buffers for each I/O operation, improving performance for applications that reuse the same buffers.

# [RETURN VALUE](#RETURN_VALUE)

None

# [ERRORS](#ERRORS)

The CQE *res* field will contain the result of the operation, the number of bytes read on success. On error, a negative errno value is returned.

# [NOTES](#NOTES)

This function accepts an array of iovec's with a size\_t number of bytes each, but io\_uring\_cqe's result code is an \_\_s32 value, so in theory a short read with a large enough iov\_len value could generate an ambiguous return. But the number of bytes actually transferred has the same limit as [**read**(2)](/man/os/liburing/read.2) so this cannot happen in practice.

# [SEE ALSO](#SEE_ALSO)

[**io\_uring\_get\_sqe**(3)](/man/os/liburing/io_uring_get_sqe.3), [**io\_uring\_submit**(3)](/man/os/liburing/io_uring_submit.3), [**io\_uring\_prep\_readv**(3)](/man/os/liburing/io_uring_prep_readv.3), [**io\_uring\_prep\_readv2**(3)](/man/os/liburing/io_uring_prep_readv2.3), [**io\_uring\_prep\_read\_fixed**(3)](/man/os/liburing/io_uring_prep_read_fixed.3), [**io\_uring\_prep\_writev\_fixed**(3)](/man/os/liburing/io_uring_prep_writev_fixed.3), [**io\_uring\_register\_buffers**(3)](/man/os/liburing/io_uring_register_buffers.3)

January 18, 2025 liburing-2.10

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Document: io_uring_prep_readv_fixed(3) from liburing 2.15-r4 (Chainguard OS)
Source: https://github.com/axboe/liburing.git